Bipolar electrostatic chucks are commonly used in semiconductor wafer fabrication. These chucks use electrostatic forces to hold a semiconductor wafer in place during the manufacturing process. Over time, the chucks develop wear from use and their performance degrades.
An exemplary electrostatic chuck will be described with reference to FIGS. 1A-1B and FIGS. 2A-2B.
FIG. 1A shows a plan view of front side 102 of exemplary electrostatic chuck 100. Front side 102 has a mounting ledge 104 and a top surface 106. Top surface 106 is elevated above mounting ledge 104 as seen in FIG. 1B. Mounting ledge 104 is used to mount electrostatic chuck 100 during use. Mounting ledge 104 may have mounting holes (not shown) to secure electrostatic chuck 100 during use. Mounting ledge 104 may also be modified in any other known fashion to secure electrostatic chuck 100 during use.
Top surface 106 comprises a first electrode portion 108 and a second electrode portion 110. First electrode portion 108 is further divided into an outer electrode ring 112 and an inner electrode portion 114. Second electrode portion 110 is a ring of aluminum and is electrically separated from first electrode portion 108 via dielectric epoxy 116. Dielectric epoxy 116 also retains second electrode portion 110 within first electrode portion 108.
In FIG. 1B, the uppermost portion of front side 102 is anodized to prevent unwanted oxidation and provide a dielectric surface of specific thickness between electrostatic chuck 100 and a semiconductor wafer when in use. Outer electrode ring 112 and mounting ledge 104 have associated anodized surface 118, second electrode 110 has associated anodized surface 120, and inner electrode portion 114 has associated anodized surface 122. Also seen in FIG. 1B is access path 126, a way of electrically connecting second electrode portion 110 through first electrode portion 108.
FIG. 2A shows a plan view of back side 200 of electrostatic chuck 100. There are four sections shown on back side 200. Two of these sections are anodized, outer anodized portion 208 and inner anodized portion 210. The other two sections are bare aluminum, outer aluminum portion 206 and inner aluminum portion 204. Before the anodization process, sections 204 and 206 are prevented from being anodized by coating sections 204 and 206 with a masking substance. After the anodization process, the mask is removed. On inner aluminum portion 204 access path 126 can be seen.
In operation, electrostatic chuck 100 uses electrostatic forces to hold a semiconductor wafer to its surface. As shown in FIG. 1B, first electrode portion 108 and second electrode portion 110 are oppositely charged. First electrode portion 108 is positively charged and second electrode portion 110 is negatively charged. This charge is developed by applying a voltage difference between first electrode portion 108 and second electrode portion 110. The charges of the two portions of electrostatic chuck 100 induce an opposite charge in a nearby portion of a semiconductor wafer, which creates an electrostatic attraction between the semiconductor wafer and electrostatic chuck 100.
When processing of the semiconductor water is completed, the voltage applied to first electrode portion 108 and second electrode portion 110 may be removed or partially reversed to “dechuck” the wafer. Because of the fragility of the wafer and the precision required in all aspects of the fabrication process, very precise control of the electric fields produced by the electrostatic chuck is required. Accordingly, all parameters of the electrostatic chuck that may affect the electric fields produced, must be maintained within a precise range. Non-limiting examples of these intrinsic characteristics include resistance, inductance, capacitance, and impedance of the electrostatic chuck.
Use of electrostatic chuck 100 over time may degrade its performance. The degradation may occur as a result of surface affects that may develop with use, as shown in FIG. 3. FIG. 3 shows a cross-sectional view of an exemplary electrostatic chuck 300. Electrostatic chuck 300 shows various signs of wear. Electrostatic chuck 300 has front side 302, which comprises mounting ledge 304 and top surface 306. Top surface 306 has first electrode portion 312 and second electrode portion 310. First electrode portion 312 is separated from second electrode portion 310 by a dielectric epoxy 316. The upper portion of top surface 306 has an anodized layer 318 disposed thereon.
Several types of wear may develop on electrostatic chuck 300. Particulate matter 320 and 322 may stick to top surface 306. Scratches or marks 324 and 326 may occur in anodized layer 318. Pits 328 and 330 may also develop in dielectric epoxy layer 316. Deep scratches 332 may occur in top surface 306 such that the scratch penetrates anodized layer 318 and affects first electrode portion 312. Particulate matter 320 and 322 may be removed from the surface of electrostatic chuck 300 by known methods of cleaning, but scratches 324 and 326, pits 328 and 330, and deep scratches 332 require more intensive repair.
When an electrostatic chuck becomes too worn to use, it may be refurbished to repair the wear developed in use. Conventionally, such a process requires separation of the two electrodes 402 and 404 of electrostatic chuck 400 as seen in FIG. 4. By separating electrodes 402 and 404, the entire epoxy layer that separated the two electrodes may be removed and replaced. Disassembly of an electrostatic chuck is very difficult and may cause irreparable damage to the electrostatic chuck. When electrode 404 is removed from the recess in electrode 402, the epoxy left as residue on both electrodes must be fully removed. This removal may damage one or both of electrodes 402 and 404. Also, the epoxy is generally removed by means of scraping, which may damage either or both of electrodes 402 and 404.
Further, improper reassembly after such a refurbishing process is also very likely to compromise the working parameters of an electrostatic chuck. Specifically, when second electrode 404 is placed back in recess 406 in electrostatic chuck 400, it may scratch or be scratched by the edges of recess 406. A point of contact may also be formed between the wall of recess 406 and second electrode 404, causing a failure of the refurbishing process. Also, if the upper surface of second electrode 404 is not flush with the upper surface of first electrode 402, the height mismatch may negatively affect the performance of electrostatic chuck 400 or may even render the resulting device unusable.
During reassembly, a new epoxy layer must be added to electrostatic chuck 400 to separate electrodes 402 and 404. Improper application of this new epoxy layer is very difficult. If there is too little epoxy applied, the upper surface of second electrode 404 will end tip lower than the upper surface of electrode 402, which may negatively affect the performance of electrostatic chuck 400. If there is too much epoxy applied, the upper surface of electrode 404 will end tip higher than the upper surface of electrode 402, which may negatively affect the performance of electrostatic chuck 400. Also if the reassembly is not carefully controlled, air bubbles may form between electrodes 402 and 404 or the epoxy layer and either electrode 402 or electrode 404. These air bubbles may negatively affect the performance of electrostatic chuck 400.
In light of the various potential problems associated with the conventional techniques for refurbishing a bipolar electrostatic chuck discussed above, the typical yield of such techniques is only approximately 30%.
What is needed is a bipolar electrostatic chuck refurbishing process that is less likely to damage the bipolar electrostatic chuck.
What is additionally needed is a bipolar electrostatic chuck refurbishing process that provides a yield greater than 30%.